Responses of Soybean (Glycine max L.) Varieties to Rhizo bia inoculation and Phosphorus Fertilizer Application at Mettu, Southwestern Ethiopia

Abstract

Soybean (Glycine max (L.) Merril) is an important legume crop in terms of production and global trade. Soybean is an inexpensive and high quality source of protein for resource poor families and can be used for edible oil production in Ethiopia. Due to limited availability of phosphorus in the soil of Metu area, as a result of soil acidity and lack of compatible rhizobia, yield of soybean in this area was very low. Therefore, this study was initiated to determine the responses of soybean varieties to rhizobia inoculation and phosphate fertilizer application rates on some important growth, root and nodulation and yield and yield components at Metu, southwestern Ethiopia. The experiment was conducted at Metu subcenter, maremiya bet site of the Jimma Agricultural Research Center in the 2018 main cropping season. The experiment consisted of eighteen treatment combinations of three factors: i.e., two inoculation treatments (inoculation with the Rhizobia strain of SB-MAR- 1495 and non-inoculated), three levels of phosphate fertilizer (0, 20, 40 kg P ha-1 in the form of TSP) and three soybean varieties (Afgat, Clark 63K and SCS-1) using Randomized Complete Block Design in factorial arrangement with three replications. The total nitrogen and available phosphorus after harvest showed slight increase from the initial soil result although; it is categorized in the different ratings. Significant (p<0.01) interaction effects of variety, rhizobia inoculation and phosphate rate for all growth, nodulation characteristic and yield and yield components. Varieties showed significant (p<0.01) influence for all Phenological, growth, root, nodulation and yield and yield components. Phosphorus rates had significant (p<0.01) influence for all growth, root, nodulation and yield and yield components, phenologically on days to 90% physiological maturity. Also seed inoculation with rhizobia strains had significant (p<0.01) influence for phenologically on days to 90% physiological maturity, growth, root, nodulation and yield and yield components. Significant influence on plant height, leaf area, number of nodules per plant, nodule effectiveness, nodule dry weight, taproot length, and number of pods per plant, number of seed per pods, grain yield, hundred seed weight, dry biomass, harvest index and phosphorus uptake efficiency were recorded from the interaction of rhizobia inoculation and 40 kg P ha-1fertilizer application rate . Significant and positive correlations were found for all growth, root and nodulation parameters with grain yield. Yield was highly significantly and positively correlated with dry biomass (r=0.81), plant height (r=0.67) and hundred seed weight (r=0.65).The combined application of the Rhizobia strain (SB-MARK 1495) and 40 kg p ha-1 produced significantly better nodulation and yield than the rest of the treatments. Afgat variety should better results on growth, nodulation and yields of plant height, number of nodules and grain yields. Therefore, the use of rhizobia SB-MARK 1495 and 40 kg p ha-1 found important in increasing nodulation, P uptake, dry biomass and yield of soybean in the study area. The application of inoculated rhizobia and 40 kg P ha-1 produced the highest net benefit 34098ETB ha-1. The highest marginal rate of return (3641%) was obtained from yield at inoculated rhizobia and 40 kg P ha-1 of Afgat soybean variety was the most profitable treatment .However, as the study was conducted only for one season and one location, it needs to be repeated over seasons and locations for valid recommendations.